A combine harvester is a machine that is used to harvest grain crops. The objective is to complete several processes, which traditionally were distinct, in one pass of the machine over a particular part of the field. Among the crops that may be harvested with a combine are wheat, oats, rye, barley, corn, soybeans, flax or linseed, and others. The waste (e.g., straw) discharged on the field includes the remaining dried stems and leaves of the crop which may be, for example, chopped and spread on the field as residue or baled for feed and bedding for livestock.
A combine harvester cuts crop using a wide cutting header. The cut crop may be picked up and fed into the threshing and separating mechanism of the combine, typically consisting of a rotating threshing rotor or cylinder to which grooved steel bars commonly referred to as rasp bars or threshing elements may be bolted. These rasp bars thresh and aid in separating the grains from the chaff and straw through the action of the drum against the concaves, i.e., shaped “half drum,” that may also be fitted with steel bars and a meshed grill, through which grain, chaff and smaller debris may fall, whereas the straw, being too big or long, is carried through to the outlet. The chaff, straw, and other undesired material are returned to the field via a spreader mechanism.
In an axial flow combine, this threshing and separating system serves a primary separation function. The harvested crop is threshed and separated as it is conveyed between a longitudinally arranged rotor and the inner surface of an associated chamber comprising threshing and separating concaves, and a rotor cage or cover. The cut crop material spirals and is conveyed along a helical path along the inner surface of the chamber until substantially only larger residue remains. When the residue reaches the end of the threshing drum, it is expelled out of the rear of the combine. Meanwhile, the grain, chaff, and other small debris fall through the concaves and grates onto a cleaning device or shoe. For ease of reference, this smaller particulate crop material that contains the grain and chaff is referred to as threshed crop. The grain still needs to be further separated from the chaff by way of a winnowing process.
Clean grain is separated out of the threshed crop be way of a flat oscillating cleaning system that can include a chaffer and sieves. Generally, the cleaning system operates by mechanical and pneumatic methods; blowing air through the threshed crop to winnow the chaff and then sieving the grain to separate the grain from other particulates. Clean grain that is separated from residue via the sieves is typically transported to a grain tank in the combine for temporary storage. The grain tank is typically located atop the combine and loaded via a conveyer that carries clean grain collected in the cleaning system to the grain tank.
The conventional grain tank is arranged such that grain conveyed from the cleaning system fills the tank while inclines in the tank floor allow the grain to be gravity-fed into a transversely-oriented cross auger. By virtue of gravity feed and cross auger, grain may be distributed to a single point in the grain tank, such that another conveying system can offload the grain from the grain tank. Offloading the grain is typically implemented in one of either two conveying systems. One type of offload system is a turret style system. The turret style system incorporates a vertical auger within a vertical tube. At the top of the vertical tube, an unload tube, which may include a horizontal auger, connects and pivots coextensive with the vertical tube. A long-top unload tube may be used during the harvest to unload grain to a support trailer or vehicle. The other offload system is a swivel system. The swivel system incorporates an unloading auger attached to the cross auger, angled upward from the vehicle and pivots at the side of the vehicle to offload grain. The grain in a swivel system may too collect in a support trailer or vehicle. Both systems allow large quantities of grain to be offloaded in the field without needing to stop harvesting when the grain tank fills.
In some harvests, the combine harvester will harvest grain with a support trailer or truck, which may be driven alongside. Because the typical grain tank is small compared to the size of the harvest, grain that collects temporarily in the grain tank must be conveyed to the supporting truck or trailer. The distance between the grain tank in a supporting trailer or vehicle determines the necessary length of the unload tube. For safety reasons, the supporting vehicle should not be too close to the combine during the harvest. For example, where a supporting vehicle is traveling alongside the combine, the distance between the combine and the supporting vehicle should be greater than the distance that a cutting header of the combine extends laterally from the combine. As wider cutting headers are used, longer unload tubes become necessary.
Often it is desirable to have a large grain tank. For example, when a combine is operated without a support vehicle or where a combine is temporarily separated from a support vehicle, it is desirable to allow the combine to continue harvesting and loading the grain into the grain tank. One problem with the conventional gravity fed grain tank is that the geometry of the grain tank is limited and defined by the angle of repose of the grain being collected—that is, the minimum angle of the tank floor from horizontal needed to overcome internal friction and the natural ability of grain to form a mound. The conventional grain tank cannot have a substantially flat tank floor, because grain will not be conveyed by gravity to the cross auger for unloading. Instead, a conventional grain tank floor must be substantially inclined on either side of the cross auger (e.g. fore and aft side walls). The amount of inclination needed is determined by the properties of the grain and specifically its angle of repose. Because the angle of repose is relatively steep, it can be difficult to fit a large conventional grain tank within the conventional layout of a combine harvester, while still making effective use of space within the constraint of the vehicle chassis. While placing a cross auger in the middle of the grain tank can allow for a larger grain tank for a given width, it is often necessary in typical designs to use two cross augers to allow a grain tank to have the aspect ratio necessary for fitting in a typical combine geometry.
One problem with this conventional grain tank geometry is inefficient use of the volume of the grain tank relative to the available space in the combine harvester. A further problem with some of these conventional grain tank geometries is that the inlet to the unloading system is located relative to the cross auger, which is typically located in the center of the grain tank. This limitation can restrict the available length of the unload tube. Another problem with some conventional grain tank geometries is that multiple cross augers can require a more complicated vertical conveying system for extracting the grain from the grain tank.